I'm sure about cutting the Hughes rockers - it tells you EXACTLY where they'll break. There are places in the engine where a sharp edge is a bad idea (piston dome) but harmless. Where that cut was taken is the worst possible place to remove any metal (the center of a span stressed in tension), and more so leaving a sharp negative profile with a violent change in cross-section.
If you absolutely have to remove metal there, cut only to the minimum depth to assure clearance (don't be surprised if some rockers need more than others - an extrusion or casting isn't accurate from the mold down to .001"), then blend & radius the cut into the parent shape in all directions so that the original cut is invisible. I would polish it, but that's just my OCD.

in my opinion, a large diameter "ball nose" endmill would work good for clearancing rocker arms, instead of the sharp tip, normal, endmills usually used. less blending needed, and no sharp corners created, causing potential stress risers. has anyone done it this way ? if not, why ?

This^^^

I had a special end mill mad u just to clearance
rockers if they needed it.. was a 1 1/2" with
a 1/8" radius at the bottom.. I could do a small
plunge cut in one shot

I imagine lots of people do it that way. I always use a bullnose or ball end end mill when cutting an area that will have tensile stress. That is just a common design practice.

Fly cutter with a generous radius

Funny with really high lift you can't start in the center of the valve, unless you plan on using the retainer as part of the rocker path too. Lol

It's not only a function of lift, but the actual length (not the rocker ratio) of the valve-side lever is X-important. A really long rocker (Gen-1 hemi exhaust) is moving almost vertically with low lift with a very short scrub path.

If you think you have to grind or cut the rocker arms, discover the real problem and fix that.

STICKY THIS SENTENCE^^^^^^^^^^^^^^

/THREAD

The "real problem" is apparently bad rocker arms. Way too often, they try to make a small change in an existing product (Olds V8 to Windsor, BBC to Ford L6) to save R&D, but they don't have anyone on staff competent to say "wait a minute, there are other differences...". Rocker arm geometry (not application) was settled engineering 300 years ago, they're not paying attention.
Don't modify them? Throw them away? And replace them with what? Ask the manufacturer "do these fit?" What answer do you think you'll get? Is Barton, T&D, and Jesel the answer for everyone?

We have tolerated crap from even the most expensive sources far too long to expect NEVER to get a part that needs adjustment, etc.

[/rant]